The present invention relates to a boom structure for an agricultural implement.
Conventionally, agricultural implements of this type, such as e.g. an agricultural sprayer, comprise a boom structure having mounted thereon discharge channel intended for the discharge of a desired substance in liquid or in solid form. In many cases the boom structure consists of two sections and is advanced across the field with one section protruding laterally from each side of a central frame, which is typically mounted on a tractor or a tractor-drawn trailer. The boom structure is normally constructed such that each of the two boom sections can be pivoted from a working position to a transport position. According to the length of the boom sections, they may be composed of a plurality of short subsections in the longitudinal direction.
It is well-known that during driving with such agricultural implements where the boom sections may have a length of up to e.g. 25 m, strong oscillations of the boom sections can occur, in a horizontal plane as well as in a vertical plane, and therefore various types of shock absorbing mechanisms are frequently incorporated, as is explained e.g. in European Patent Application No. 343 547.
To limit oscillations in the horizontal plane, i.e. oscillations where the outer end of the boom sections reciprocates in the travelling direction, it has previously been proposed either to connect the frame and the support via a shock absorbing device, as described in the above-mentioned European patent, or alternatively to transfer pivoting movements of one boom section to the other boom section, as is explained in British Patent Application No. 2 151 891.
All the previously known solutions, however, have been found to be inexpedient and costly. Moreover, they have been found not to be suitable for use in the situations where the agricultural implement is solely provided with one boom section arranged so as to protrude from one side of the tractor. Accordingly, there is a need for providing a simplified boom structure where the forwardly and rearwardly directed oscillations in the horizontal plane are limited effectively using relatively simple means.
When the pivot link, which connects the boom section with the central frame, comprises two link parts which are interconnected by shock absorbing means that are activated by mutual pivoting of the two link parts, e.g. in the form of a plurality of rubber blocks, it has surprisingly been found possible to provide an extremely compact pivot link structure which is easy to service, and which can moreover exhibit well-defined resilience and isolation properties. Further, in agricultural implements having two boom sections, the invention allows one boom section to the isolated from the other, it being intended to absorb the oscillations to the greatest extent possible in the pivot link between the boom section and the central frame. This structure enables the boom sections to pivot independently of each other when e.g. starting and braking the agricultural implement, and makes it possible to absorb these oscillations.
If a plurality of shock absorbing means is used, these may advantageously exhibit different characteristics and be placed such that various resilience and isolation conditions may be achieved, according to the mutual pivoting between the first link part and the second link part. For example, some of the shock absorbing means may be positioned such that they are activated only by a relatively great pivoting movement, e.g. when the boom section swings with a great amplitude. These shock absorbing means may e.g. exhibit a relatively great rigidity.
When the boom section may also be connected with the other link part so that it may pivot about a substantially horizontally extending axis, an enhanced degree of freedom is achieved in a simple manner, as regards positioning of the boom section in the use of the agricultural implement.
The invention also relates to a pivot link for an agricultural implement as stated in claim 10.
In this connection, shock absorbing means are taken to mean means which either act as a spring, a damper or as a combination thereof.